[Python] Make sure the received function is a user-defined function

These tips can be used when you want to check "Is the given function really a user-implemented function?" When creating a library in Python.

First determine if it is a function

Needless to say this.

import inspect
inspect.isfunction(func)

Determine if it is a built-in function or frozen function

In Python, you can use the built-in functions written in C language and the frozen functions built into the Python processing system in the form of bytecode among the standard libraries written in Python. For example, builtins.sorted () is a built-in function and zipimport.zipimporter () is a frozen function.

How to use sys.modules

This is relatively straightforward, but it looks for a module object with func defined in sys.modules. If it doesn't have the __file__ attribute, it's a built-in function or a frozen function. (Except for built-in modules and frozen modules, Python always has a one-to-one correspondence with files.)

modname = func.__module__
mod = sys.modules[modname]
fname = getattr(mod, '__file__', None)
return fname != None

How to use the code object

There are the following methods as other methods. I think this is more concise.

co = getattr(func, '__code__', None)
return co != None

Determine if it is a user-created function

I think there are several ways, but here if you get the path of the file where the function is defined and it is located under the __main__ module path (working directory for STDIN), then in the existing library It is determined that the file is created by the user. Note that this decision may not work for package managers (such as pyflow) that put the library cache under the working directory. Also, it may not work if you are doing ʻimport while changing the working directory using ʻos.chdir etc. (I don't know if there is such a program)

filename = path.abspath(co.co_filename)
return filename.startswith(path.join(get_maindir(), ''))

def get_maindir():
    mm = sys.modules['__main__']
    fname = getattr(mm, '__file__', None)
    if fname == None:
        # STDIN
        return os.getcwd()
    else:
        return path.dirname(path.abspath(mm.__file__))

All source code

import sys
import os
import inspect
from os import path
def is_userfunc_b(func):
    if not inspect.isfunction(func):
        return False
    modname = func.__module__
    mod = sys.modules[modname]
    fname = getattr(mod, '__file__', None)
    if fname == None:
        return false
    fname = path.abspath(fname)
    return fname.startswith(path.join(get_maindir(), ''))
    
def is_userfunc(func):
    if not inspect.isfunction(func):
        return False
    co = getattr(func, '__code__', None)
    if co == None:
        return False
    # Check that the file is placed under main module
    filename = path.abspath(co.co_filename)
    return filename.startswith(path.join(get_maindir(), ''))

def get_maindir():
    mm = sys.modules['__main__']
    fname = getattr(mm, '__file__', None)
    if fname == None:
        # STDIN
        return os.getcwd()
    else:
        return path.dirname(path.abspath(mm.__file__))